Some medical conditions have as a symptom or detrimental effect loss or reduction of tactile sensitivity of the skin of the individual. Often such medical conditions result in loss of tactile sensory perception over a period of time rather than abrupt loss of touch sensitivity. Thus, it is beneficial to have instruments which can measure the tactile sensitivity of the individual with sufficient accuracy to be able to track the tactile sensitivity of the individual over time and compare tactile sensitivity of the individual to other individuals exhibiting the same or related conditions.
One general category of tactile sensory instrument known in the art is an elongate monofilament or similar resilient elongate flexible structure which can be forced axially against the skin of the individual until the filament buckles. The filament is designed to always apply substantially the same force before the filament buckles. The filament is sufficiently elastic that when the load is removed the filament returns to its original orientation. The filament is of a type which provides a maximum force before buckling. Thus, if the user of the instrument applies the filament against the skin with too much force, it will still buckle when this maximum force is exerted on the instrument, so that the instrument never applies a force greater than this threshold force to the skin of the individual.
If the individual can feel this force (also quantifiable in terms of pressure) such tactile sensitivity can be noted in the individual's file. Various different body parts, and particularly extremities of the individual can be tested in this way and records gathered. Different testing instruments having different filaments with different threshold forces before buckling can be utilized to determine the point at which the individual no longer has sufficient tactile sensitivity to feel the loads applied by the device.
Examples of such prior art systems include U.S. Pat. Nos. 3,662,744 and 5,492,132. Prior art filament based tactile sensory perception monitoring tools benefit from having the filament be protected in some way when not in use. The filament can become damaged when merely placed in a pocket of a user or otherwise left exposed. Once the filament has been damaged it is no longer applying the proper force before buckling and so can lead to poor data being collected. Prior art filament based tactile sensory instruments have been provided by the inventor to provide such filament protection as well as systems for controlling an amount that the filament extends from a housing for application of a variable force (or pressure). Examples of such devices include U.S. Pat. Nos. 5,823,969, 6,196,976 and 6,234,977. While such retractable tactile sensory instruments have addressed the problem of protecting the monofilament to some extent, the filament remains in a position where it can catch on a shirt pocket or other holder when being stored because the filament is only re-positioned through a pivoting motion partially out of danger of potential contact and damage to the filament.
The problem of filament damage cannot be overemphasized. Often the filament can be bent or otherwise damaged in a manner which is substantially imperceptible visually or in use of the instrument. Thus, the instrument appears to be completely functional and accurately calibrated to apply the expected force. In reality, such an instrument that has been slightly damaged can be applying an improper lower or higher force (most typically lower), leading to improper diagnosis. Accordingly, a need exists for a tactile sensory evaluation instrument which has a filament that can be retracted in a manner which provides a high reliability that the filament will remain protected while retracted.